Review Article |
Corresponding author: Marcelo Ricardo Vicari ( vicarimr@yahoo.com.br ) Academic editor: Inna Kuznetsova
© 2018 Marcela Baer Pucci, Viviane Nogaroto, Luiz Antonio Carlos Bertollo, Orlando Moreira-Filho, Marcelo Ricardo Vicari.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Pucci MB, Nogaroto V, Bertollo LAC, Moreira-Filho O, Vicari MR (2018) The karyotypes and evolution of ZZ/ZW sex chromosomes in the genus Characidium (Characiformes, Crenuchidae). Comparative Cytogenetics 12(3): 421-438. https://doi.org/10.3897/CompCytogen.v12i3.28736
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Available data on cytotaxonomy of the genus Characidium Reinhardt, 1867, which contains the greatest number of species in the Characidiinae (Crenuchidae), with 64 species widely distributed throughout the Neotropical region, were summarized and reviewed. Most Characidium species have uniform diploid chromosome number (2n) = 50 and karyotype with 32 metacentric (m) and 18 submetacentric (sm) chromosomes. The maintenance of the 2n and karyotypic formula in Characidium implies that their genomes did not experience large chromosomal rearrangements during species diversification. In contrast, the internal chromosomal organization shows a dynamic differentiation among their genomes. Available data indicated the role of repeated DNA sequences in the chromosomal constitution of the Characidium species, particularly, in sex chromosome differentiation. Karyotypes of the most Characidium species exhibit a heteromorphic ZZ/ZW sex chromosome system. The W chromosome is characterized by high rates of repetitive DNA accumulation, including satellite, microsatellite, and transposable elements (TEs), with a varied degree of diversification among species. In the current review, the main Characidium cytogenetic data are presented, highlighting the major features of its karyotype and sex chromosome evolution. Despite the conserved karyotypic macrostructure with prevalent 2n = 50 chromosomes in Characidium, herein we grouped the main cytogenetic information which led to chromosomal diversification in this Neotropical fish group.
Chromosomal differentiation, Cryptic species, Repetitive DNA, Speciation genes
Crenuchidae (Teleostei: Characiformes) include 18 genera and 95 species (
Phylogenetic analysis removed these fishes from the Characidae along with the Crenuchinae, and this group was organized in a new monophyletic family, the Crenuchidae (
Based on morphological data, Characidium zebra Eigenmann, 1909 is the most ancestral species of the genus as well as also of Characidiinae (
Another common characteristic in cytogenetic data of Characidium is the occurrence of cryptic species (
Table
Representative karyotype of Characidium fasciatum with 2n = 50 chromosomes. Cytogenetic data revealed 32 m + 18 sm, without heteromorphic sex chromosomes: a conventionally Giemsa-stained b sequentially C-banded chromosomes. Scale bar: 5 µm.
Interstitial telomeric sites (ITS), which are usually correlated with chromosomal fusions, were identified in the karyotypes of Characidium schubarti Travassos, 1955, Characidium lanei Travassos, 1967, Characidium lauroi Travassos, 1949, Characidium timbuiense Travassos, 1946, Characidium serrano Buckup & Reis, 1997, and two populations of C. pterostictum (
Generally, the constitutive heterochromatin has a preferential distribution in the pericentromeric regions in the most Characidium chromosomes, but some large interstitial and terminal blocks were also observed. Chromosomal mapping of 18S and 5S rDNAs showed varied autosomal positions among Characidium genomes, ranging from single to multiple sites (Table
In fishes, tandem or dispersed repetitive DNA sequences are relevant markers for clarifying karyotype evolution and sex chromosome differentiation (
Despite the highly conserved karyotype structure, the genomes of Characidium species display a dynamic pattern of their internal chromosomal composition (Table
Distinct microsatellites also had a wide distribution in autosomal pairs (Fig.
The available data point to the substantial role of repeated DNA sequences in the chromosomal constitution of Characidium species. However, due to the extension of the existing repetitive elements, additional investigations must address their significance in the evolutionary history of Characidium and, particularly, in sex chromosome differentiation.
Fluorescence in situ hybridization using distinct classes of repeated DNA sequences as probes: In a karyotype of C. lauroi submitted to (TTAGGG)n probing (red) b karyotype of C. gomesi evidencing U2 snRNA sites (red) c Karytype of C. heirmostigmata submitted to (GATA)n probing (red) and d karyotype of C. gomesi evidencing Tc1/Mariner mapping (red). Scale bar: 10 µm.
Several Neotropical fish species are carriers of supernumerary or B chromosomes (
B chromosomes, ranging from one to four chromosomes, were described in several Characidium species (Table
Meiotic analyses revealed the bivalent pairing of the ZW chromosomes, as well as the bivalent plus one univalent formation in specimens carrying three B chromosomes (
The occurrence of a ZZ/ZW sex chromosome system is another karyotypic characteristic of Characidium genomes. It was first described by
The majority of microsatellites sites were located in the terminal region of the Z chromosome and in the terminal/centromeric regions of W chromosome. The exception is (TTA)10, which was widely distributed throughout the whole W chromosome, and (GAG)10, which had a preferential accumulation in the W and B chromosomes of C. alipioi (
18S rDNA sequences are also particular components of many Characidium sex chromosomes, occupying the short and the long arms of Z and W chromosomes, respectively, or the long arms of both sex chromosomes (Table
Idiograms showing main characteristics already identified for the ZZ/ZW sex chromosome system in Characidium species. It was highlighted the position of the centromere, distribution of euchromatin and heterochromatin, W-specific probes, and rDNA sites. The a column detaches the species carrying 18S rDNA sites on the short and long arms of the Z and W chromosomes, respectively; the b column highlights the species bearing 18S rDNA sites on the long arms of both Z and W chromosomes; the c column shows the species that do not present 18S rDNA sequences on either Z or W chromosomes; the d column presents the species bearing Z and W chromosomes with unusual characteristics, including morphology, 18S and 5S rDNA sites, and W-specific probe distribution.
Later differentiations in such protosex chromosomes were gradually acquired by isolated populations, leading to deletions and duplications in the rearranged regions due to meiotic pairing failures. Thus, recombination suppression mechanisms (rearrangements, heterochromatinization, repeated DNA accumulation and gene erosion) were naturally selected, giving rise to distinct heteromorphic W chromosomes (
The current sympatric occurrence of some Characidium species does not display hybridization events among them. Sympatric and syntopic pairs of Characidium species, with the presence or absence of sex chromosomes, had already been described, namely C. alipioi and Characidium sp. cf. C. lauroi (
Schematic idiograms showing some steps proposed in the differentiation process of the ZZ/ZW sex pair. The origin of the ZZ/ZW sex pair from the protosex chromosome of the Characidium species. Centromeric region (blue); 18S rDNA site (green); W specific probe region (red); probable Z speciation genes region (purple).
Review of Characidium cytogenetic studies until 2018. The variation in the diploid number (2n) is due to the presence of B chromosomes. “Unknown” signifies that the data was not available in the original study. NOR: Nucleolar Organizer Region; M: Metacentric; SM: Submetacentric; ST: Subtelocentric; A: Acrocentric. * The chromosome pairs are not indicated in the original publication.
Species | Localization | 2n | Sex chromosome system | Karyotype formula | rDNA 18S | rDNA 5S | References |
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C. alipioi Travassos, 1955 | Ribeirão Grande Stream, SP, Brazil | 50 | ZZ/ZW | 30M+20SM | Pair 16 (NOR) | Unknown |
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Ribeirão Grande Stream, SP, Brazil | 50–54 | ZZ/ZW | 32M+18SM | Pair 18 | Pair 20 |
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C. fasciatum Reinhardt, 1867 | Rio São Francisco, MG, Brazil | 50 | ZZ/ZW | 32M+18SM | Unknown | Unknown |
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C. cf. fasciatum | Rio das Velhas Stream, MG, Brazil | 50 | ZZ/ZW | Unknown | Unknown | Unknown |
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C. gomesi Travassos, 1956 | Paiol Grande Stream, SP, Brazil | 50 | ZZ/ZW | ♂ 32 M+18 SM | Pair 18 | Unknown |
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♀ 31 M+19SM | |||||||
C. gomesi (cited like C. cf. fasciatum) | Paranapanema, SP, Brazil | 50–54 | ZZ/ZW | 32M+18SM | Three autossomic pairs* | Unknown |
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C. gomesi | Pardo River, SP, Brazil | 50–54 | ZZ/ZW | 32M+18SM | Pair 17 and an additional chromosome (NOR) | Unknown |
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Machado River, MG, Brazil | 50 | Absent | 32M+18SM | Pair 17 (NOR) | Unknown |
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C. cf. gomesi | Quebra Perna Stream, PR, Brazil | 50 | ZZ/ZW | ♂ 32 M+18 SM | Pairs 4, 7 and 17 | One autosomal pair* |
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♀31M+18SM+1ST | |||||||
Alambari Stream, SP, Brazil | 50 | ZZ/ZW | ♂ 32 M+18 SM | ZW | Pairs 20 and 25 |
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♀ 31 M+19SM | |||||||
Novo River, SP, Brazil | 50–54 | ZZ/ZW | ♂ 32 M+18 SM | Pair 18 | Pair 25 |
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♀ 31 M+19SM | |||||||
C. gomesi | Verde River, PR, Brazil | 50 | ZZ/ZW | ♂ 32 M+18 SM | Pairs 17, 22 and in one of the homologous of the pairs 1 and 20 | Unknown |
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♀31+18SM+1ST | |||||||
C. cf. gomesi | Rio da Cachoeira Stream, GO, Brazil | 50 | ZZ/ZW | 32M+18SM | Unknown | Unknown |
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Magdalena Stream, SP, Brazil | 50–52 | ZZ/ZW | 32M+18SM | Unknown | Unknown |
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C. gomesi | Grande River, SP, Brazil | 50 | ZZ/ZW | 32M+18SM | Pair 17 | Unknown |
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Minhoca Stream, MG, Brazil | 50 | ZZ/ZW | 32M+18SM | Pair 17 | Unknown |
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Tietê River, SP, Brazil | 50 | ZZ/ZW | 32M+18SM | ZW | Unknown |
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São Domingos River, MG, Brazil | 50 | ZZ/ZW | 32M+18SM | Pair 17 | Unknown |
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Vermelho River, MT, Brazil | 50 | ZZ/ZW | 32M+18SM | Pair 17 | Unknown |
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São João River, PR, Brazil | 50 | ZZ/ZW | ♂ 32 M+18 SM | Pairs 10 and 17 | Unknown |
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♀31M+18SM+1ST | |||||||
C. heirmostigmata da Graça & Pavanelli, 2008 | Barra Grande River, PR, Brazil | 50 | ZZ/ZW | 32M+18SM | Pair 4 | Pair 19 |
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C. lagosantense Travassos, 1947 | Amendoim Stream, MG, Brazil | 50 | Absent | Unknown | Unknown | Unknown |
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C. cf. lagosantense | Infernao Lagoon, SP, Brazil | 50 | Unknown | 32M+18SM | Unknown | Unknown |
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C. lanei Travassos, 1967 | Barroca River, PR, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | ZW | One autosomal pair* |
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Cari Stream, PR, Brazil | 50 | ZZ/ZW | 32M+18SM | ZW (NOR) | One autosomal pair* |
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C. lauroi Travassos, 1949 | Grande River, SP, Brazil | 50 | ZZ/ZW | ♂ 32 M+18 SM | ZW (NOR) | Unknown |
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♀31M+18SM+1ST | |||||||
C. oiticicai Travassos, 1967 | Pairaitinguinha River, SP, Brazil | 50–53 | ZZ/ZW | 32M+18SM | ZW (NOR) | Unknown |
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C. orientale Buckup & Reis, 1997 | Chasqueiro Stream, RS, Brazil | 50 | ZZ/ZW | 32M+18SM | ZW | Pairs 1, 3, 5, 6, 20 and W |
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C. pterostictum Gomes, 1947 | Betari River, SP, Brazil | 50–53 | ZZ/ZW | 32M+16SM+2A | ZW | Unknown |
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Faú River, SP, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | ZW | Unknown |
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Cari River, PR, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | ZW | Unknown |
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Jacareí River, PR, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | ZW | Unknown |
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Itapocu River, SC, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | ZW | Unknown |
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Pairiquera-Açú River, SP, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | ZW | Pairs 9, 11 and 13 |
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Jacuí River, RS, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | ZW | Three autosomal pairs* |
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Itapeva Lagoon, RS, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | Unknown | Unknown |
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Carlos Botelho Ecological Station, SP, Brazil | 50 | Unknown | 32M+16SM+2ST | Unknown | Unknown |
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C. rachovii Regan, 1913 | Cabeças Stream, RS, Brazil | 50 | ZZ/ZW | 32M+18SM | ZW | Pairs 1, 3 ,5, 17, 20 and W |
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C. schubarti Travassos, 1955 | Cinco Réis River, PR, Brazil | 50 | ZZ/ZW | 32M+18SM | ZW (NOR) | Unknown |
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C. serrano Buckup & Reis, 1997 | Canoinha Stream, RJ, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | Unknown | Unknown |
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C. stigmosum Melo & Buckup, 2002 | Ave Maria River, GO, Brazil | 50 | Absent | 32M+18SM | Pair 23 | Pairs 1, 7 and 17 |
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C. tenue (Cope, 1894) | Chuí Stream, SC, Brazil | 50 | Absent | 32M+18SM | Pair 23 | Pairs 1 and 7 |
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C. timbuiense Travassos, 1946 | Valsugana Velha Stream, ES, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | ZW | Three autosomal pairs* |
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C. vestigipinne Buckup & Hahn, 2000 | Caraguatá River, RS, Brazil | 50 | ZZ/ZW | 32M+18SM | ZW | Pairs 1, 17 and 20 |
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C. vidali Travassos, 1967 | Bananeiras Stream, RJ, Brazil | 50 | ZZ/ZW | 32M+18SM | One autosomal pair* | W chromosome and in one autosomal pair* |
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C. aff. vidali | Bananeiras Stream, RJ, Brazil | 50–54 | ZZ/ZW | 32M+18SM | Pair 21 | Pairs 5, 12 and 20 |
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C. xavante da Graça, Pavanelli & Buckup, 2008 | Xingu River, MT, Brazil | 50 | Absent | 32M+18SM | Pair 23 | Pairs 1, 7 and 17 |
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C. zebra Eigenmann, 1909 | Jatai Reservoir, SP, Brazil | 50 | Unknown | 32M+18SM | Pair 25 (NOR), with 1 to 2 additional pairs | Unknown |
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C. cf. zebra | Passa Cinco River, SP, Brazil | 50 | Unknown | 32M+18SM | Pair 23 | Pair 17 |
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Passa Cinco River, SP, Brazil | 50–51 | Unknown | Unknown | Unknown | Unknown | Venere et al. (1999) | |
Piracicaba River, SP, Brazil | 50 | Unknown | 32M+18SM | Pair 25 (NOR) | Unknown |
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Ribeirão Claro Stream, SP, Brazil | 50 | Absent | Unknown | Unknown | Unknown |
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Pairaitinga River, SP, Brazil | 50 | Absent | 32M+18SM | Pair 23 | Pairs 1, 6, and 17 |
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Paiol Grande Stream, SP, Brazil | 50 | Absent | 32M+18SM | Pair 23 (NOR) | Unknown |
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Machado River, MG, Brazil | 50 | Absent | 32M+18SM | Pair 23 (NOR) | Unknown |
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Alambari River, SP, Brazil | 50 | Absent | 32M+18SM | Pair 23 | Pair 17 |
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Novo River, SP, Brazil | 50 | Absent | 32M+18SM | Pair 23 | Pair 17 |
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Araquá River, SP, Brazil | 50 | Absent | 32M+18SM | Pair 23 | Pair 17 |
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Duas Antas Stream, MT, Brazil | 50 | Absent | 32M+18SM | Pair 23 | Pairs 1 and 17 |
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Juba River, MT, Brazil | 50 | Absent | 32M+18SM | Pair 23 | Pairs 1, 6, 9, 17 and 18 |
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C. aff. zebra | Corredeira Stream, SP, Brazil | 50 | Absent | 32M+18SM | Pairs 4, 7 and 23 | Pair 17 |
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Corredeira Stream, SP, Brazil | 50 | Absent | 32M+18SM | Pairs 2, 4, 7, 20, 23 and 17 | Pair 17 |
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Characidium sp. | Preto River, SP, Brazil | 50 | ZZ/ZW | 32M+18SM | ZW (NOR) | Unknown |
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Lagoon of the Corredeira Stream, SP, Brazil | 50 | ZZ/ZW | 32M+16SM+2A | ZW | Pairs 3, 7, 8, 23 and 24 |
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Characidium sp.2 | Vermelho River, MT, Brazil | 50 | ZZ/ZW | 32M+18SM | W and pair 7 | Pair 17 |
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Characidium sp. | Formoso River, GO, Brazil | 50 | ZZ/ZW | 32M+18SM | Unknown | Unknown |
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Inferno Lagoon, SP, Brazil | 50 | Unknown | 32M+18SM | Unknown | Unknown |
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Characidium sp.1 | Russo River, MT, Brazil | 50 | ZZ/ZW | 32M+18SM | Pair 7 | Pair 17 |
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Characidium sp.3 | Arinos River, MT, Brazil | 50 | ZZ/ZW | 32M+18SM | Pair 1 | Pair 1 |
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Characidium sp.4 | Nanay River, Peru | 50 | ZZ/ZW | 32M+18SM | Pair 7 | Pair 18 |
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Characidium sp.5 | Canoinha Stream, RS, Brazil | 50 | ZZ/ZW | 32M+18SM | Pair 19 | Pairs 1, 5 and 6 |
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Fish cytogenetic and molecular studies have improved over the last few years, especially with regard to better identification of the karyotypic evolution and sex chromosome differentiation among different groups of fish, as well as genes or specific regions related to sex determination. W-specific repetitive probes were already constructed for Characidium using microdissection from female metaphase chromosomes and degenerate oligonucleotide-primed PCR (DOP-PCR) or whole genome amplification (WGA) protocols. These probes were later applied to chromosome painting in Characidium using a C. gomesi W-specific probe (
The ZZ/ZW sex chromosome system is well-known and described. The repeated DNA classes related to gene erosion and differentiation of W chromosome, as well as regions or genes implicated in sex determination and gonadal differentiation, have not yet been properly investigated in most species. It has been demonstrated that the repeated DNA sequences are closely related to the regulatory genes network, particularly TEs, in a process called molecular co-option or exaptation (
In other pathways, sequencing procedures of particular W fractions is needed for investigating specific genes related to sex determination and differentiation. Indeed, integrating cytogenetic, genomic, molecular, and bioinformatic tools will be essential for a better understanding of sex determination and differentiation processes in fishes, with applications in ecological and evolutionary studies.
Chromosomal diversification in Characidium here revised show a diversified karyotype microstructure despite its conserved karyotypic macrostructure with prevalent 2n of 50 chromosomes arranged in 32 m + 18 sm. Differences in the number of rDNA sites, in heterochromatin blocks, in B chromosomes number and, in sex chromosomes sizes, as well as an interesting dynamic of repetitive DNAs on the chromosomes are observed among species, leading to chromosomal diversification and speciation. The data showed that different microsatellite expansions are involved in the sex chromosome differentiation in Characidium. In addition, the microsatellite (TTA)10 play an important role in gene degeneration and erosion on the W chromosome in some Characidium species. These data are important for the molecular characterization of the W and B chromosomes, to karyotype structures determination and comprehension of cryptic species. Future studies integrating cytogenetic, genomic and molecular data open perspectives to understand the sex determination, B chromosome composition and, “speciation genes” in Characidium genomes.
The authors are grateful to Instituto Chico Mendes de Conservação da Biodiversidade (protocol number SISBIO 15117) for authorizing the capture of specimens. This study was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Secretaria de Ciência e Tecnologia do Estado do Paraná (SETI), and Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Estado do Paraná (Fundação Araucária).